1. Field of the Invention
This invention relates to reducing power consumption of integrated circuits. More particularly, the invention relates to reducing power consumption in MEMS devices, particularly power loss caused by transistor current leakage even while the MEMS-based device is in a low-power or standby mode.
2. Background of Related Art
Wireless mobile terminals continue to decrease in overall size with advances in integrated circuit fabrication and in circuit design. At the same time, power output has increased, with an attendant increase in power consumption. The reduction in size limits the size of battery that can reasonably be incorporated without adversely affecting the size of the unit. It is therefore becoming more critical to reduce unnecessary power consumption as the size of the units decreases.
Low-power or standby modes are commonly provided to reduce power consumption when no call is in progress. However, the extent to which power consumption can be reduced in a low-power or standby mode is limited by the presence of unwanted leakage currents. Whilst proper design of the active devices can reduce leakage currents, they cannot be eliminated entirely in this way. Moreover, as integrated circuits become smaller, the design problem of reducing leakage currents is likely to become more difficult.
FIG. 3 illustrates a conventional integrated circuit capable of operating in a standby or low-power mode.
In particular, as shown in FIG. 3, an integrated circuit 300 includes an operating circuit portion 301, and a low power control circuit portion 302. The low power control circuit 302 places the operating circuit 301 into a low power or standby mode as appropriate for the particular application. The low power control circuit 302 also monitors activity for instructions to awake the operating circuit 301 from its low power state.
When the conventional operating circuit 301 is placed into a quiescent or low power state, various transistor switches 310 are opened to electrically separate the operating circuit 301 from one or more power sources.
As wireless mobile terminals become smaller and more powerful, the amount of energy used during low-power or standby mode becomes more critical. Previous attempts to overcome this problem have involved setting each transistor or active device into a mode in which it consumes the least power. However, the reality is that all transistors have some amount of leakage current even when turned off, no matter how minute. As the number of transistors in integrated circuits increase with added miniaturization and complexity, more transistors are required, adding to an overall power leakage. Moreover, it becomes increasingly difficult to provide the required hardware registers and to develop appropriate controlling software to set all the necessary transistors into a low-power state, and to awake the same when coming out of the low power mode.
Clearly, much of the foregoing applies not only to mobile wireless terminals, but to a greater or lesser extent to battery operated electronic equipment of any kind, and particularly to equipment employing complex integrated circuits, having components that consume large amounts of power, such as for transmitting, and having a need to standby in readiness between uses.
There is a need for reducing even further both the complexity of low-power controlling requirements and the leakage of transistors within an integrated circuit during low power (e.g., standby) modes.
In accordance with the principles of the present invention, an integrated circuit (IC) chip is provided with a xe2x80x98power-savexe2x80x99 switch, including MEMS (Micro-Electro-Mechanical Systems) switches in each power and ground ring, to be used to open the circuit and eliminate power drain.
The MEMS switches are preferably latched in position by, for example, a permanent magnet, at least when in the open position, so that no power is required to keep the switches open.
When the equipment of which the IC forms a part is put on standby, it enters a low-power mode in which the xe2x80x98power-savexe2x80x99 switch in each IC is actuated by a small control circuit that remains powered up.
The invention is applicable to chips used in wireless mobile terminals, where power consumption is critical and it is necessary to enter a standby mode between uses.